Intravenous drug users who get antiviral drugs may reduce their risk of HIV infection, according to a new study published in the British medical journal The Lancet. The landmark study shows that AIDS can be prevented in every population group at risk.

"This is an important study that opens up an additional option for preventing HIV in a hard-to-reach population," Dr. Joseph McGowan, medical director of the Center for AIDS Research and Treatment at North Shore University Hospital in Manhasset, N.Y., told HealthDay News.

The study followed 2,400 drug users in Thailand over four years. Roughly half were assigned an antiviral drug, tenofovir, in a practice known as pre-exposure prophylaxis, or PrEP. Others were given a placebo. Those who took the antiviral drug reduced their chances of infection by 49 percent, and those who took the pills most regularly were 74 percent less likely to become infected.

Injection drug use is believed to be the cause of one in 10 new HIV infections worldwide. But in parts of Eastern Europe and central Asia where injection drug use is higher, up to 80 percent of new HIV infections are caused by intravenous drug use, HealthDay reports.

McGowan says the study’s strategy in conjunction with other prevention methods could be vital to reducing HIV transmission among this population.

"Adoption of this strategy, not as a stand-alone, but in conjunction with needle exchange, counseling, opiate substitution, social support and mental health therapy may enable us to get ahead of this expanding epidemic," McGowan said.

Participants in the study were heavily monitored by nurses and given modest payments to stay in the trial – a strategy that most drug users won’t be exposed to.

“We should be under no illusions that these were real-world settings,” Mitchell Warren, executive director for AVAC, an organization that lobbies for AIDS prevention, told the New York Times.

McGowan agrees. Services like those provided in the trial along with monthly HIV testing and condom distribution might not occur outside a clinical trial setting, so the outcomes may not be as good, he told HealthDay News.

Despite the challenges the study presents, its results mark a pivotal moment in HIV prevention. “This is an exciting day,” Dr. Jonathan Mermin, director of HIV prevention for the Centers for Disease Control and Prevention in Atlanta, told the New York Times. “This culminates a decade of PrEP research.”